Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions						1 Months Ended	3 Months Ended
	Jun. 01, 2021	Apr. 30, 2020	Mar. 13, 2020	Mar. 01, 2020	Jan. 08, 2020	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							3,156,250		3,006,250
Carrying value							$ 31,563		$ 30,063
Liquidation value and redemption price per share (in dollars per share)							$ 10,000
Aggregate liquidation value							$ 31,900
Series Y
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							0		0
Carrying value							$ 0		$ 0
Issue date							Feb. 12, 2015
Contractual rate in effect				6.125%			0.00%
Dividend declared per share (in dollars per share)							$ 0	$ 153.13
Preferred stock, redeemed				$ 1,430
Series Y | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Mar. 01, 2020
Series AA
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							142,500		142,500
Carrying value							$ 1,425		$ 1,425
Issue date							Jun. 04, 2015
Contractual rate in effect							6.10%
Dividend declared per share (in dollars per share)							$ 152.50	152.50
Series AA | Subsequent Event | Forecast
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect	6.10%
Preferred stock, redeemed	$ 1,400
Series AA | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Sep. 01, 2020
Series BB
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							115,000		115,000
Carrying value							$ 1,150		$ 1,150
Issue date							Jul. 29, 2015
Contractual rate in effect							6.15%
Dividend declared per share (in dollars per share)							$ 153.75	153.75
Series BB | Subsequent Event | Forecast
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect	6.15%
Preferred stock, redeemed	$ 1,200
Series BB | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Sep. 01, 2020
Series DD
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							169,625		169,625
Carrying value							$ 1,696		$ 1,696
Issue date							Sep. 21, 2018
Contractual rate in effect							5.75%
Dividend declared per share (in dollars per share)							$ 143.75	143.75
Series DD | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Dec. 01, 2023
Series EE
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							185,000		185,000
Carrying value							$ 1,850		$ 1,850
Issue date							Jan. 24, 2019
Contractual rate in effect							6.00%
Dividend declared per share (in dollars per share)							$ 150.00	150.00
Series EE | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Mar. 01, 2024
Series GG
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							90,000		90,000
Carrying value							$ 900		$ 900
Issue date							Nov. 07, 2019
Contractual rate in effect							4.75%
Dividend declared per share (in dollars per share)					$ 150.42		$ 118.75	150.42
Series GG | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Dec. 01, 2024
Series JJ
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							150,000		0
Carrying value							$ 1,500		$ 0
Issue date							Mar. 17, 2021
Contractual rate in effect							4.55%
Dividend declared per share (in dollars per share)					$ 0
Series JJ | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Jun. 01, 2026
Series I
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							293,375		293,375
Carrying value							$ 2,934		$ 2,934
Issue date							Apr. 23, 2008
Dividend declared per share (in dollars per share)							$ 93.06	132.44
Series I | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.00035%
Series I | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Apr. 30, 2018
Series Q
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							150,000		150,000
Carrying value							$ 1,500		$ 1,500
Issue date							Apr. 23, 2013
Contractual rate in effect							5.15%
Dividend declared per share (in dollars per share)							$ 128.75	128.75
Series Q | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0325%
Series Q | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							May 01, 2023
Series R
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							150,000		150,000
Carrying value							$ 1,500		$ 1,500
Issue date							Jul. 29, 2013
Contractual rate in effect							6.00%
Dividend declared per share (in dollars per share)							$ 150.00	150.00
Series R | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.00033%
Series R | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Aug. 01, 2023
Series S
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							200,000		200,000
Carrying value							$ 2,000		$ 2,000
Issue date							Jan. 22, 2014
Contractual rate in effect							6.75%
Dividend declared per share (in dollars per share)							$ 168.75	168.75
Series S | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0378%
Series S | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Feb. 01, 2024
Series U
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							100,000		100,000
Carrying value							$ 1,000		$ 1,000
Issue date							Mar. 10, 2014
Contractual rate in effect							6.125%
Dividend declared per share (in dollars per share)							$ 153.13	153.13
Series U | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0333%
Series U | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Apr. 30, 2024
Series V
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							250,000		250,000
Carrying value							$ 2,500		$ 2,500
Issue date							Jun. 09, 2014
Dividend declared per share (in dollars per share)							$ 85.97	130.73
Series V | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0332%
Series V | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Jul. 01, 2019
Series X
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							160,000		160,000
Carrying value							$ 1,600		$ 1,600
Issue date							Sep. 23, 2014
Contractual rate in effect							6.10%
Dividend declared per share (in dollars per share)							$ 152.50	152.50
Series X | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0333%
Series X | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Oct. 01, 2024
Series Z
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							200,000		200,000
Carrying value							$ 2,000		$ 2,000
Issue date							Apr. 21, 2015
Contractual rate in effect		5.30%
Dividend declared per share (in dollars per share)		$ 265.00					$ 101.24	132.50
Series Z | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.00038%
Series Z | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							May 01, 2020
Series CC
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							125,750		125,750
Carrying value							$ 1,258		$ 1,258
Issue date							Oct. 20, 2017
Contractual rate in effect							4.625%
Dividend declared per share (in dollars per share)							$ 115.63	115.63
Series CC | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							three-month LIBOR
Preferred stock dividend rate, variable, basis spread							0.0258%
Series CC | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Nov. 01, 2022
Series FF
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							225,000		225,000
Carrying value							$ 2,250		$ 2,250
Issue date							Jul. 31, 2019
Contractual rate in effect							5.00%
Dividend declared per share (in dollars per share)							$ 125.00	125.00
Series FF | Term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							Term SOFR
Preferred stock dividend rate, variable, basis spread							0.0338%
Series FF | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Aug. 01, 2024
Series HH
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							300,000		300,000
Carrying value							$ 3,000		$ 3,000
Issue date							Jan. 23, 2020
Contractual rate in effect							4.60%
Dividend declared per share (in dollars per share)			$ 125.22				$ 115.00	$ 125.22
Series HH | Term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							Term SOFR
Preferred stock dividend rate, variable, basis spread							0.03125%
Series HH | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Feb. 01, 2025
Series II
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)							150,000		150,000
Carrying value							$ 1,500		$ 1,500
Issue date							Feb. 24, 2020
Contractual rate in effect							4.00%
Dividend declared per share (in dollars per share)						$ 0	$ 100.00
Series II | Term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis							Term SOFR
Preferred stock dividend rate, variable, basis spread							0.02745%
Series II | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date							Apr. 01, 2025